Systems and methods for security sensing in a power cable for an article of merchandise

ABSTRACT

Embodiments of the present invention are directed to merchandise security systems and methods for displaying and protecting an article of merchandise from theft. In one example, the system includes a sensor configured to be secured to the article of merchandise, wherein the sensor includes alarming circuitry. The system also includes a tether comprising a pair of conductors electrically connected to the alarming circuitry, wherein the pair of conductors is configured to transfer power to the sensor and/or to the article of merchandise. In response to power ceasing to be transferred, the alarming circuitry is configured to monitor an electrical signal transmitted through the pair of conductors in order to determine whether the tether has been cut or removed from the sensor.

CROSS REFERENCE To RELATED APPLICATION

This application is a continuation of U.S. application Ser. No. 15/111,626, filed Jul. 14, 2016, which is a 371 National Stage Entry of International Application No. PCT/US2015/012378, filed Jan. 22, 2015, which claims the benefit of priority to U.S. Provisional Application No. 61/930,529 filed on Jan. 23, 2014, the entire disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to security systems and methods for displaying articles of merchandise in a retail environment. More particularly, the invention relates to systems and methods for security sensing in a tether for an article of merchandise.

BACKGROUND OF THE INVENTION

Retailers routinely display articles of merchandise, such as telephones, portable computers (e.g. notebooks, laptops, tablets, etc.), e-readers, media players, and the like for customers to evaluate before making a purchase. These articles of merchandise are continually being made smaller and lighter in weight due to advances in technology and materials. As a result, such merchandise is increasingly vulnerable and susceptible to theft. At the same time, the retail price, and hence the profit margin, for such merchandise continues to decline. Accordingly, these articles of merchandise need to be secured by a security device that effectively and cost efficiently protects the merchandise from theft.

It is common in the field of retail merchandise security to tether electronic devices to a store fixture to prevent theft, yet still allowing a customer to interact with the device. The retailers and their customers want these tethers to be as unobtrusive as possible, making smaller diameter tethers desirable. One problem with keeping tether size small is the number of conductors needed to supply power and sensing signals. Typically, a plurality of conductors is needed to provide both power and security. As a result, reducing the number of conductors while maintaining necessary functionality and security can be challenging.

SUMMARY OF THE INVENTION

In one aspect, the invention is a merchandise security system for displaying and protecting an article of merchandise. The system includes a sensor configured to be secured to the article of merchandise, wherein the sensor including alarming circuitry. The system further includes a tether including a pair of conductors electrically connected to the alarming circuitry, wherein at least one of the pair of conductors is configured to transfer power to the sensor and/or to the article of merchandise. In response to power ceasing to be transferred, the alarming circuitry is configured to monitor an electrical signal transmitted through the pair of conductors in order to determine whether the tether has been cut or removed from the sensor.

In one embodiment, the pair of conductors consists of a positive power conductor and a negative ground conductor. In another embodiment, the tether is coupled to a recoiler such that the tether is extendable and retractable relative to the recoiler. In yet another embodiment, each of the sensor and the recoiler has at least one resistor electrically connected to the pair of conductors in a sense loop circuit, and the alarming circuitry is configured to determine a change in resistance in the sense loop circuit. In still another embodiment, the alarming circuitry and the pair of conductors define the sense loop circuit, and the resistor in the recoiler is disposed across the pair of conductors. In still another embodiment, the alarming circuitry is configured to generate a visual and/or an audible alarm signal in response to the sensor being removed from the article of merchandise, the tether being removed from the sensor, and/or the tether being cut.

In another aspect, the invention is a method for displaying and protecting an article of merchandise. The method includes transferring power through a tether to a sensor attached to the article of merchandise and/or to the article of merchandise, wherein the tether includes a pair of conductors electrically connected to the sensor. The method further includes monitoring, in response to power ceasing to be transferred, an electrical signal transmitted through the pair of conductors in order to determine whether the tether has been cut or removed from the sensor.

In one embodiment monitoring includes repeatedly determining a voltage level in predetermined increments of time. In another embodiment, determining includes determining whether the voltage level is greater than a predetermined voltage level. In yet another embodiment, the method further includes generating a visual and/or an audible alarm signal when the voltage level is greater than the predetermined voltage level. In still another embodiment, the method further includes repeating the step of determining the voltage level if the voltage level is greater than the predetermined voltage level. In still another embodiment, the method further includes generating the electrical signal on the pair of conductors prior to determining the voltage level. In still another embodiment, monitoring includes determining a change in total resistance in a sense loop circuit defined at least by the sensor, the pair of conductors, and a plurality of resistors. In still another embodiment, the method further includes determining whether the pair of conductors has been shorted.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The detailed description of the invention provided hereafter may be better understood with reference to the accompanying drawing figures, in which embodiments of a merchandise security system for displaying an article of merchandise are disclosed, and in which like reference characters indicate the same or similar parts.

FIG. 1 is a perspective view of a merchandise security system for displaying and protecting an article of merchandise according to an embodiment of the invention.

FIG. 2 is a perspective view of another embodiment of a merchandise security system according to the invention shown with the article of merchandise and a sensor attached thereto removed from a base.

FIG. 3 is a perspective view showing the merchandise security system of FIG. 2 electrically connected to a recoiler secured to a support surface of a display fixture and electrically connected to an external source of power.

FIG. 4 is a perspective view of the merchandise security system of FIG. 3 showing the recoiler detached from a mounting plate secured to the support surface of the display fixture.

FIG. 5 is an exploded perspective view showing an embodiment of a sensor for use with a merchandise security system according to the invention.

FIG. 6 is an exploded perspective view of the sensor of FIG. 5 shown with an upper portion of the sensor attached to an article of merchandise and a lower portion of the sensor detached from the upper portion.

FIG. 7 is a perspective view of another embodiment of a sensor for use with a merchandise security system according to the invention shown with an upper portion of the sensor detached from a lower portion of the sensor.

FIG. 8 is a perspective view of a portion of the merchandise security system of FIG. 1 illustrating the use of a key to arm and/or disarm the alarming circuitry of the sensor.

FIG. 9 is a schematic illustrating a pair of conductors configured for transmitting electrical power to the sensor and/or the article of merchandise according to the invention.

FIG. 10 is a schematic illustrating a sense loop circuit for generating an alarm signal according to the invention.

FIG. 11 is a graph depicting the voltage in the sense loop circuit of FIG. 10 when a tether is intact and there is a loss of electrical power.

FIG. 12 is a graph depicting the voltage in the sense loop circuit of FIG. 10 when the tether has been cut or removed.

FIG. 13 is a graph depicting the voltage in the sense loop circuit of FIG. 10 for an intact and connected tether, referred to as a “good cable,” and a cut or removed tether, referred to as a “bad cable.”

FIG. 14 is a graph depicting an example of the voltage in the sense loop circuit of FIG. 10 where the voltage level is initially at an input power level and thereafter the input power ceases.

FIG. 15 is a graph depicting another example of the voltage in the sense loop circuit of FIG. 10 where the voltage level is initially at the input power level and thereafter input power ceases.

FIG. 16 is a flowchart of a method for displaying and protecting an article of merchandise according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

One or more embodiments of a merchandise security system for displaying an article of merchandise are shown in the accompanying drawing figures and described below. The article of merchandise, indicated generally herein by reference character M, is typically a display model or an operational sample of electronic merchandise, such as portable telephones, smart phones, computers (e.g. notebooks, laptops, tablets, etc.), e-readers, media players, and the like, for a customer to examine before making a decision whether to purchase the article. The article of merchandise is typically displayed in a manner that permits a prospective purchaser to evaluate the operation and features of the merchandise, while protecting the merchandise from theft. In one embodiment, a sensor with alarming circuitry may be attached to the article of merchandise for detecting various alarming conditions, such as the article being removed from the sensor. A tether may be operably engaged with the sensor at one end, while the opposite end may be secured to a base or to a surface of a display fixture. As explained in further detail below, the alarming circuitry of the sensor may also be configured to detect an alarming condition of the tether, such as a cutting, severing, removing or detaching of the tether. As also explained in further detail below, the tether may consist of only a pair of conductors. Thus, unlike conventional tethers that include three, four, or more conductors, the tether according to one embodiment may have only two conductors for providing both power and security functionality. Regardless, the alarming circuitry is configured to monitor an electrical signal in the conductors in order to determine if an alarming condition has occurred.

FIGS. 1-4 illustrate embodiments of a merchandise security system, indicated generally herein by reference character 10, for displaying an article of merchandise M and securing the merchandise from theft or unauthorized removal. The system 10 generally includes a sensor 12, a tether 14, a base 16, and a recoiler 18, as shown in the embodiment of FIGS. 2-4. The sensor 12 is configured to be secured to the article of merchandise M, such as with a pressure-sensitive adhesive. Alternatively, or in addition, the sensor 12 may be secured to the article of merchandise M by two or more retaining arms 34, as illustrated in the embodiment of FIG. 1. A first end of the tether 14 may be electrically connected to the recoiler 18, as shown in FIG. 4, while the opposite second end of the tether may include a jack or connector 22 for electrically connecting the tether to the sensor 12, as shown in FIG. 2. Thus, connector 22 may be releasably engaged with sensor 12 to establish electrical communication therebetween. The connector 22 may be further secured in position with a lock mechanism 21, such as a clip, as indicated by the arrow in FIG. 2. As such, when lock mechanism 21 is engaged with connector 22, the connector may not be removed from the sensor 12 without first disengaging the lock mechanism. The lock mechanism 21 may allow tension to be applied to the tether 14 without causing the connector 22 to become inadvertently disconnected from the sensor 12. Furthermore, the lock mechanism 21 may provide stress relief for the electrical connection between the sensor 12 and the tether 14.

The base 16 is configured to removably support the sensor 12 thereon such that a prospective purchaser may remove the article of merchandise M and the sensor secured thereto from the base for inspection, and subsequently return the merchandise to the base for display. The base 16 may define an opening 15 therethrough that allows the tether 14 to extend and retract relative to the base. Recoiler 18 may be disposed within the base 16, or alternatively, the recoiler may be secured below a support surface 20 (e.g., a counter, shelf, or the like) of a display fixture, as shown in FIG. 3. In this regard, the recoiler 18 may include a mounting plate 23 that is configured to be secured to the underside of the support surface 20, in which case the recoiler is configured to engage the mounting plate and be secured thereto. As shown in FIG. 3 and illustrated schematically in FIG. 10, the recoiler 18 may be electrically connected to a power source 24 via an input power cable 25 that is configured to provide power to the recoiler and to the tether 14. A plug or other connector, for example, an AC power plug and AC/DC power converter, may be disposed at a first end of the input power cable 25 for electrically connecting the input power cable to an external source of electrical power, for example, a conventional 110V AC power outlet. A second opposite end of the input power cable 25 may be electrically connected to an input cable 27 of the recoiler 18. In some embodiments, the sensor 12 is also electrically connected to a power cable 26 that is configured to provide electrical power to the article of merchandise M, as shown in FIG. 2. Thus, the power cable 26 may be utilized to facilitate demonstration of the operation of the article of merchandise M on display, as well as for charging a rechargeable battery of the merchandise. FIG. 2 further shows that the power cable 26 may include a connector 28 that is configured to operably engage an input port provided on the article of merchandise M. In some embodiments, the alarming circuitry of the sensor 12 may be configured to detect removal of the connector 28 and to generate an audible and/or a visual alarm signal in response to removal of the connector 28 from the sensor 12.

As discussed above, the sensor 12 may include alarming circuitry, a processor, a central processing unit, or the like, that is configured to determine whether various security events have occurred for generating an audible and/or a visual alarm signal. The sensor 12 may also include an alarm (e.g., a piezoelectric device) that is configured to generate an audible alarm. Thus, the sensor 12 may be configured as “alarm-on-product,” whereby the sensor is operable to alarm when attached to the article of merchandise M and/or when detached from the article of merchandise. In some cases, the sensor 12 may include a visual indicator (e.g., an LED) for indicating the alarming circuitry is armed and/or alarming. Moreover, the sensor 12 may include a transfer port 30 that is configured to communicate with a key 32 (see, FIG. 8) for arming and/or disarming the alarming circuitry. In one embodiment, the transfer port 30 is configured to communicate wirelessly with key 32 to determine whether the key is authorized to arm and/or disarm the alarming circuitry. According to some embodiments, the key 32 is similar to that described in U.S. Pat. No. 7,737,845, the contents of which are hereby incorporated by reference in their entirety. According to one embodiment, the sensor 12 may include a contact, limit or pressure switch 33 (see, FIG. 7), or the like, that is configured to detect when the article of merchandise M has been removed from the sensor. The alarming circuitry may be configured to detect the removal of the article of merchandise M from the sensor 12 and to generate and an audible and/or a visual alarm signal in response thereto.

In some embodiments, the sensor 12 is a one-piece design that is configured to be attached to the article of merchandise M. FIGS. 5-8 illustrate embodiments wherein the sensor 12 may include an upper portion 35 and a lower portion 37. The upper portion 35 may be configured to be secured to the lower portion 37, such as with a proprietary fastener 39. In addition, the upper portion 35 may be configured to be secured to the article of merchandise M, while the lower portion 37 may be configured to receive the connector 22. FIG. 7 shows that a first end of the power cable 26 may be enlarged and configured to be inserted into a recess 31 formed in the lower portion 37, which secures the power cable therein when the upper portion 35 and the lower portion 37 are secured together. In addition, FIG. 6 shows that upper portion 35 may include an engagement member 40 and FIG. 7 shows that lower portion may include an opening 42 configured to receive the engagement member therein. Engagement between the engagement member 40 and the opening 42 may be used to align the upper portion 35 and the lower portion 37 relative to one another prior to securing the upper and lower portions together.

Furthermore, FIGS. 1, 5-6, and 8 illustrate that sensor 12 may include one or more retaining arms 34 for securing the article of merchandise M to the sensor. In one example, FIG. 5 shows that the upper portion 35 may include a pair of slots 36 that are each configured to receive a respective retaining arm 34 therein. Thus, retaining arms 34 may be configured to slide within the slots 36 to adjust the position of the retaining arms relative to the width or length of the article of merchandise M. As illustrated by FIGS. 5-6, the lower portion 37 may be secured to the upper portion 35 such that the retaining arms 34 are secured therebetween and cannot be removed without first detaching the lower portion from the upper portion.

Embodiments of the present invention provide for the delivery of electrical power to the article of merchandise M and/or to the sensor 12 through a pair of conductors 50 (see, e.g., FIG. 9) disposed within the tether 14 (removed for purposes of clarity). In some examples, the tether 14 includes only two conductors 50, such as a positive power line and a ground line. An input power source 24 may be in electrical communication with the conductors 50 for transmitting power through the tether 14 and to the article of merchandise M and/or the sensor 12. In order to obtain a sense signal using only the power lines, one technique is to simply detect when the electrical power stops flowing. The problem with this method is that the sensor 12 and/or the article of merchandise M typically do not receive power when there is a power outage, which could cause a false alarm in the merchandise security system 10. Instead, one embodiment of the invention provides security sensing over the same conductors 50 used to supply power to the article of merchandise M and/or the sensor 12. As such, the diameter of the tether 14 may be reduced in comparison to conventional tethers, and the incidence of false alarms may be reduced.

According to some embodiments, the merchandise security system 10 utilizes a security scan for determining whether the tether 14 has been cut or removed from the sensor 12, and/or whether the power cable 26 has been removed from the article of merchandise M. This scan may be performed when input power is no longer being provided. In this case, the sensor 12 and associated alarming circuitry may operate on battery power for carrying out the security scan.

FIG. 10 schematically illustrates one embodiment of a sense loop circuit 55 defined between the alarming circuitry or a central processing unit (CPU) and the recoiler 18. In this embodiment, the sense loop circuit 55 includes a plurality of resistors R comprising a voltage divider network. One or more resistors R may be disposed in both the sensor 12 and the recoiler 18. The resistor R in the recoiler 18 may be disposed across the pair of conductors. The sense loop circuit 55 may be further defined by the pair of conductors 50 extending through the tether 14. If the tether is cut or disconnected, the total resistive load detected by the alarming circuitry and/or the CPU changes.

FIG. 11 shows a graph depicting the voltage in the sense loop circuit 55 when the tether 14 is intact (i.e., not cut or removed) and there is a loss of electrical power, for example as a result of a power outage. As shown, the voltage in the sense loop circuit 55 is about 1.4 volts. FIG. 12 shows a graph depicting the voltage in the sense loop circuit 55 when the tether 14 has been cut (whether partially or completely) or removed (e.g., disconnected or detached). As shown, the voltage in the sense loop circuit 55 is about 2.4 volts. Thus, the detected voltage level is higher when the tether 14 has been cut or removed (e.g., disconnected or detached). FIG. 13 shows another graph depicting the voltage in the sense loop circuit 55 where an intact and connected tether 14, indicated as a “good cable” in FIG. 13, has a lower voltage than a cut or removed (e.g., disconnected or detached) tether, indicated as a “bad cable” in FIG. 13.

In one embodiment, the security scan commences immediately after power is lost. For example, input power may be provided at about 18 volts, and when power is lost, the detected voltage would be 0 volts. The merchandise security system 10 may include capacitors that do not allow for a sudden drop in voltage, but there is typically a delay before the voltage level drops to the lower level. As the capacitors discharge, the voltage level passes from the initial input power (e.g., about 18 volts), to the “bad cable” range (e.g., about 2.4 volts), and to the “good cable” range (e.g., about 1.4 volts). If the security scan was performed immediately after the power is lost and the tether 14 was intact and connected, the “bad cable” range would be detected, and the tether would be incorrectly indicated as cut or disconnected. However, it is understood that if the scan is initiated immediately after power ceases, the alarming circuitry and/or CPU is able to compare the measured voltage level and the expected voltage level during the voltage decay period. If the measured and expected voltage levels are within a predetermined range during the decay period following a power loss, an alarm is not generated.

FIG. 14 shows a graph depicting another example of the voltage in the sense loop circuit 55 where the voltage level is initially at about 18 volts and thereafter the input power ceases at about 3.0 seconds. There is a sharp decline in the voltage level to about 6.8 volts at about 3.3 seconds. This drop may occur in about 250 ms. Then the voltage drops further to about 1.5 volts at about 5.3 seconds, wherein the further drop takes about 2 seconds. FIG. 15 shows a similar graph depicting another example of the voltage in the sense loop circuit 55 where the voltage level is initially at about 18 volts and thereafter the input power is lost. FIG. 15 demonstrates that a security scan may be initiated after a predetermined period of time and after the voltage transition so that false alarms are reduced. In this example, there is about 3 seconds after power is lost before the security scan begins.

FIG. 16 shows a flowchart of an embodiment of a method 60 for determining the integrity and connection of the tether 14 according to the present invention. In the illustrated embodiment, the alarming circuitry and/or CPU may be configured to initially determine whether a voltage level is equal to about “X” volts, as indicated by reference character 62. For example, “X” volts may be the normal input voltage provided, such as about 18 volts. If the voltage is equal to “X” volts, there is no alarm event. If the voltage does not equal “X” volts, a security scan is initiated, as indicated by reference character 64. The security scan may be cyclical in that the scan may be performed repeatedly in predetermined increments of time. The security scan may be initiated immediately after power ceases, or alternatively, after a predetermined delay (e.g., about 2-4 seconds), as discussed above, to allow the voltage in the tether 14 to decay. The security scan may first determine whether the tether 14 has been shorted (e.g., the conductors 50 are crimped together), as indicated by reference character 66. In the case that the tether 14 is shorted, the voltage level will be zero, or close to zero, and an alarm signal will be generated, as indicated by reference character 76. In one embodiment, a cycle of the security scan may be about 200 ms in duration to determine whether the tether 14 is shorted.

If the tether 14 is not shorted, the alarming circuitry or CPU may generate an electrical signal on the pair of conductors 50, as indicated by reference character 68. For example, the electrical signal could be a ping, current, pulse, frequency, or the like. In one embodiment, generating an electrical signal may include setting the bit high on one of the conductors 50 to the alarming circuitry and/or CPU and waiting for the tether 14 to charge. For example, the bit may be set to about 3.0 volts. FIGS. 11 and 13 show that the bit may be set high at time “T1” and then a pause is effectuated (e.g., about 250 ms). The voltage level in the tether 14 is then determined, and if the voltage level is greater than “Y” volts (e.g., about 2.0 volts), as indicated by reference character 70, the security scan is repeated at least one more time, as indicated by reference character 72. If the voltage level is still greater than “Y” volts, as indicated by reference character 74, an alarm signal is generated, as indicated by reference character 76. However, if the voltage level is not greater than “Y” volts, either after the first measurement or the second measurement, the security scan is restarted, as indicated by reference character 64, and no alarm signal is generated.

It is understood that the voltage levels and scanning intervals may be any desired value in order to determine whether to generate an alarm signal and that the aforementioned values are intended only as examples to illustrate the broad principles and concepts of the invention. The determined voltage level may be analog levels (ADC readings), although other values or levels may be determined in order to perform the aforementioned method 60. In addition, it is understood that the steps of the flowchart shown in FIG. 16 are meant for illustrative purposes only and that the steps may be performed in any desired order and that certain steps may be combined or eliminated in various embodiments. For example, the step 66 of determining if the tether 14 is shorted may be eliminated, as the step 70 of determining the voltage level “Y” after the step 68 of generating an electrical signal may be used to determine if the tether 14 has been shorted.

The foregoing has described one or more embodiments of merchandise security systems and methods for displaying and protecting an article of merchandise from theft. Those of ordinary skill in the art will understand and appreciate that numerous variations and modifications of the invention may be made without departing from the spirit and broad scope of the invention. Accordingly, all such variations and modifications are intended to be encompassed by the appended claims. 

That which is claimed is:
 1. A merchandise security system for displaying and protecting an article of merchandise comprising: a sensor configured to be secured to the article of merchandise, the sensor comprising alarming circuitry; and a tether comprising a pair of conductors electrically connected to the alarming circuitry, wherein at least one of the pair of conductors is configured to transfer power to the sensor and/or to the article of merchandise, and wherein, in response to power ceasing to be transferred, the alarming circuitry is configured to monitor an electrical signal transmitted through the pair of conductors in order to determine whether the tether has been cut or removed from the sensor.
 2. The merchandise display system of claim 1, wherein the pair of conductors comprises a positive power conductor and a ground conductor.
 3. The merchandise display system of claim 1, wherein the tether is coupled to a recoiler such that the tether is extendable and retractable relative to the recoiler.
 4. The merchandise display security device of claim 3, wherein each of the sensor and the recoiler comprises at least one resistor electrically connected to the pair of conductors in a sense loop circuit, and wherein the alarming circuitry is configured to determine a change in resistance in the sense loop circuit.
 5. The merchandise display system of claim 4, wherein the alarming circuitry and the pair of conductors define the sense loop circuit, and wherein the resistor in the recoiler is disposed across the pair of conductors.
 6. The merchandise display system of claim 3, wherein an end of the tether comprises a connector configured to releasably engage the sensor.
 7. The merchandise display system of claim 1, wherein the alarming circuitry is configured to generate a visual and/or an audible alarm signal in response to the sensor being removed from the article of merchandise, the tether being removed from the sensor and/or the tether being cut.
 8. The merchandise display system of claim 1, wherein the sensor comprises a transfer port configured to facilitate wireless communication with a key for arming and/or disarming the alarming circuitry.
 9. The merchandise display system of claim 1, further comprising a base for removably supporting the sensor thereon.
 10. The merchandise display system of claim 1, wherein the tether consists of only the pair of conductors.
 11. A method for displaying and protecting an article of merchandise comprising: transferring power through a tether to a sensor attached to the article of merchandise and/or to the article of merchandise, the tether comprising a pair of conductors electrically connected to the sensor; and monitoring, in response to power ceasing to be transferred, an electrical signal transmitted through the pair of conductors in order to determine whether the tether has been cut or removed from the sensor.
 12. The method of claim 11, wherein monitoring comprises repeatedly determining a voltage level in predetermined increments of time.
 13. The method of claim 12, wherein determining comprises determining whether the voltage level is greater than a predetermined voltage level.
 14. The method of claim 13, further comprising generating a visual and/or an audible alarm signal when the voltage level is greater than the predetermined voltage level.
 15. The method of claim 13, further comprising repeating the step of determining the voltage level if the voltage level is greater than the predetermined voltage level.
 16. The method of claim 12, further comprising generating the electrical signal on the pair of conductors prior to determining the voltage level.
 17. The method of claim 11, wherein monitoring comprises determining a change in total resistance in a sense loop circuit defined at least by the sensor, the pair of conductors, and a plurality of resistors.
 18. The method of claim 17, further comprising determining whether the pair of conductors has been shorted.
 19. The method of claim 11, further comprising determining a voltage level in a sense loop circuit defined at least by the sensor and the pair of conductors. 